Electronic assemblies with solidified thixotropic thermal interface material

ABSTRACT

To accommodate high power densities associated with high performance integrated circuits, an integrated circuit package includes a heat-dissipating structure in which heat is dissipated from a surface of a die to an integrated heat spreader (IHS) through a high capacity thermal interface formed of metal that has been injected in a semi-solid state. In one embodiment, vacuum and a shear-controlled viscosity enable semi-solid metallic material to fill a narrow chamber between the die surface and a specially shaped mold plate that doubles as an IHS, without inducing voids in the solidified metal. In another embodiment, an injection machine is disclosed. Methods of fabrication, as well as application of the package to an electronic assembly and to an electronic system, are also described.

TECHNICAL FIELD

Embodiments of the inventive subject matter relate generally toelectronics packaging and, more particularly, to an electronic assemblythat includes an integrated circuit package comprising a high capacitythermal interface between the integrated circuit and a heat spreader todissipate heat generated in a high performance integrated circuit, andto manufacturing methods related thereto.

BACKGROUND INFORMATION

Integrated circuits (IC's) are typically assembled into packages byphysically and electrically coupling them to a substrate made of organicor ceramic material. One or more IC packages can be physically andelectrically coupled to a printed circuit board (PCB) to form an“electronic assembly”. The “electronic assembly” can be part of an“electronic system”. An “electronic system” is broadly defined herein asany product comprising an “electronic assembly”. Examples of electronicsystems include computers (e.g., desktop, laptop, hand-held, server,etc.), wireless communications devices (e.g., cellular phones, cordlessphones, pagers, etc.), computer-related peripherals (e.g., printers,scanners, monitors, etc.), entertainment devices (e.g., televisions,radios, stereos, tape and compact disc players, video cassetterecorders, MP3 (Motion Picture Experts Group, Audio Layer 3) players,etc.), and the like.

In the field of electronic systems there is an incessant competitivepressure among manufacturers to drive the performance of their equipmentup while driving down production costs. This is particularly trueregarding the packaging of IC's on substrates, where each new generationof packaging must provide increased performance, particularly in termsof an increased number of components and higher clock frequencies, whilegenerally being smaller or more compact in size. As the density andclock frequency of IC's increase, they accordingly generate a greateramount of heat. However, the performance and reliability of IC's areknown to diminish as the temperature to which they are subjectedincreases, so it becomes increasingly important to adequately dissipateheat from IC environments, including IC packages.

An IC substrate may comprise a number of metal layers selectivelypatterned to provide metal interconnect lines (referred to herein as“traces”), and one or more electronic components mounted on one or moresurfaces of the substrate. The electronic component or components arefunctionally connected to other elements of an electronic system througha hierarchy of electrically conductive paths that include the substratetraces. The substrate traces typically carry signals that aretransmitted between the electronic components, such as IC's, of thesystem. Some IC's have a relatively large number of input/output (I/O)terminals (also called “lands”), as well as a large number of power andground terminals or lands.

As the internal circuitry of IC's, such as processors, operates athigher and higher clock frequencies, and as IC's operate at higher andhigher power levels, the amount of heat generated by such IC's canincrease their operating temperature to unacceptable levels.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a significant need inthe art for apparatus and methods for packaging an IC on a substratethat minimize heat dissipation problems associated with high clockfrequencies and high power densities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional representation of a prior art ICpackage;

FIG. 2 illustrates a cross-sectional representation of an IC packagewith a high capacity thermal interface, in accordance with oneembodiment of the invention;

FIG. 3 illustrates a top view of a combination mold plate and integratedheat spreader (IHS), in accordance with one embodiment of the invention;

FIG. 4 illustrates a cross-sectional representation of the combinationmold plate and IHS shown in FIG. 3, taken along dashed line 121 of FIG.3;

FIG. 5 illustrates a cross-sectional representation of the combinationmold plate and IHS shown in FIG. 3, taken along dashed line 123 of FIG.3;

FIG. 6 illustrates a cross-sectional representation of a thermalinterface material (TIM) injection machine, in accordance with oneembodiment of the invention, and having a piston in a first position;

FIG. 7 illustrates a cross-sectional representation of a TIM injectionmachine, in accordance with one embodiment of the invention, and havinga piston in a second position;

FIG. 8 illustrates a top view of a metal sheet having a central troughor channel, representing a stage in the fabrication of a combination IHSand mold plate, in accordance with one embodiment of the invention;

FIG. 9 illustrates a cross-sectional representation of a fabricatingmachine having metal punches in a first position relative to thepartially fabricated IHS shown in FIG. 8, in accordance with oneembodiment of the invention;

FIG. 10 illustrates a cross-sectional representation of a fabricatingmachine having metal punches in a second position relative to thepartially fabricated IHS, in accordance with one embodiment of theinvention;

FIG. 11 illustrates a cross-sectional representation of a partiallyfabricated IHS, representing an intermediate stage in the fabrication ofa combination mold plate and IHS, in accordance with one embodiment ofthe invention;

FIG. 12 illustrates a top view of the partially fabricated IHS shown inFIG. 11;

FIG. 13 illustrates a cross-sectional representation of a skiving toolof a skiving machine being employed on the partially fabricated IHSshown in FIG. 12, in accordance with one embodiment of the invention;

FIG. 14 illustrates a cross-sectional representation of an intermediatestage in the fabrication of a combination mold plate and IHS, inaccordance with one embodiment of the invention;

FIG. 15 illustrates a top view of the partially fabricated IHS shown inFIG. 14;

FIG. 16 illustrates a cross-sectional representation of a fabricatingmachine employing a stamping tool on the partially fabricated IHS shownin FIG. 12, in accordance with one embodiment of the invention;

FIG. 17 is a block diagram of an electronic system incorporating atleast one electronic assembly with a high capacity thermal interface inaccordance with one embodiment of the invention;

FIG. 18 is a flow diagram of a method of forming thermally conductivematerial between an IC and a plate, in accordance with one embodiment ofthe invention; and

FIGS. 19A and 19B together illustrate a flow diagram of a method ofoperating a machine to form thermally conductive material between an ICand a mold plate, in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration, but not of limitation,specific embodiments of the invention. These embodiments are describedin sufficient detail to enable those skilled in the art to understandand implement them, and it is to be understood that other embodimentsmay be utilized and that structural, mechanical, compositional,electrical, and procedural changes may be made without departing fromthe spirit and scope of the present disclosure. Such embodiments of theinventive subject matter may be referred to, individually and/orcollectively, herein by the term “invention” merely for convenience andwithout intending to voluntarily limit the scope of this application toany single invention or inventive concept if more than one is in factdisclosed. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of embodiments of the presentdisclosure is defined only by the appended claims.

The inventive subject matter, in at least one embodiment, provides asolution to thermal dissipation problems that are associated with priorart packaging of integrated circuits that have high circuit density andthat operate at high clock speeds and high power levels, by employing ahigh capacity thermal material as a thermal interface between one ormore IC's and a heat spreader. Various embodiments are illustrated anddescribed herein.

In one embodiment, a front surface of an IC die is flip-chip mounted toan organic land grid array (OLGA) substrate using “controlled collapsechip connect” (C4) technology. A high capacity thermal interfacematerial is injected, in semi-solid form, between the back surface ofthe die and an integrated heat spreader (IHS). In one embodiment, thehigh capacity thermal material comprises a eutectic solder alloy. Ashaped mold plate, which doubles as the IHS, channels the semi-solidmetallic material into a narrow chamber between the die surface and themold plate. In one embodiment, a solder injection machine uses pressure,vacuum, and a viscosity-shearing mechanism to quickly inject thesemi-solid metallic material without inducing voids in the metal. Otherembodiments include methods of fabricating the mold plate, methods ofoperating the injection machine, as well as application of theelectronic assembly to an electronic system.

FIG. 1 illustrates a cross-sectional representation of a prior art ICpackage 1. IC package 1 represents a typical prior art structure thatincludes an IC die 2 mounted in “flip-chip” orientation with its lands(not shown) facing downward to couple with corresponding lands 6 on theupper surface of a substrate 4 through solder balls or bumps 5.Substrate 4 can be a one-layer board or a multi-layer board, and it caninclude additional lands 8 on its opposite surface for mating withadditional packaging structure (not shown).

Die 2 generates heat from internal structure, including wiring traces,that is located near its lower surface; however, most of the heat isdissipated through its upper surface. Heat that is concentrated withindie 2 is dissipated to a large surface that is in contact with die 2 inthe form of an integrated heat spreader (IHS) 2 that is typically formedof metal such as copper or aluminum. IHS 2 typically includes a supportmember 10 that extends downward to make physical and thermal contactwith the upper surface of substrate 4 through a thermally conductiveadhesive (not shown).

To improve the thermal conductivity between die 2 and IHS 3, a thermalinterface material 12 is often provided between die 2 and IHS 3. Thethermal interface material 12 typically is a thermal gel or greasecontaining metal particles.

To further dissipate heat from IHS 3, a heat sink 14 (optionally havingheat fins 16) is often coupled to IHS 3 to dissipate heat into theambient environment. For increased thermal conductivity between IHS 3and heat sink 14, a thermal interface material 18 is often providedbetween IHS 3 and heat sink 14. Like thermal interface material 12,thermal interface material 18 is typically a thermal gel or greasecontaining metal particles.

The IC package 1 of FIG. 1 is for most purposes no longer capable ofmeeting the thermal-dissipating requirements of today's high performanceelectronic assemblies. While the silicon die provides some lateral heatspreading, it is insufficient to appreciably reduce the peaktemperature(s). Even the high thermal conductivity of copper (which isgreater than three times that of silicon) is insufficient to handle thehot spots. If existing thermal dissipation structure is incapable ofdissipating sufficient heat to maintain the die peak temperature below aspecified value, the performance of the electronic assembly must bethrottled back by reverting to a temperature-dependent processor powercontrol process. Otherwise, the electronic assembly could malfunction orexperience a catastrophic failure. Thus, with increased heat dissipationrequirements for electronic assemblies, it has become necessary tosubstantially improve the performance of thermal interface materials andintegrated heat spreaders.

FIG. 2 illustrates a cross-sectional representation of an IC package 100with a high capacity thermal interface 122, in accordance with oneembodiment of the invention. Thermal interface 122 comprises a thermallyconductive material that has been formed between die 102 and acombination mold plate and integrated heat spreader (IHS) 120 that willbe described in greater detail regarding FIGS. 3-5.

Still referring to FIG. 2, some characteristics of thermal interface 122will now be discussed. In one embodiment, thermal interface 122comprises a eutectic solder alloy of approximately 63% tin and 37% lead.However, the specific proportions of tin and lead are not critical, anddifferent proportions can be used. In addition, many different alloyscan be used. In general, thermal interface 122 comprises an alloy fromthe group consisting essentially of tin, lead, silver, gold, nickel,copper, antimony, zinc, indium, bismuth, and gallium.

The term “essentially”, as used herein, means more than a trace amount,i.e. more than 2% by weight.

The use of metal within thermal interface 122 provides a significantlygreater thermal transfer compared with thermal gels and thermal greasescontaining metal particles, as exemplified by thermal interface 12 ofthe prior art IC package 1 of FIG. 1. However, alloys such as thosementioned above cannot be inserted in liquid form between die 102 andIHS 120 without producing significant voids resulting from the formationof dendrites and gas entrainment upon cooling. The presence of thesevoids significantly reduces the thermal transfer properties of thethermal interface material.

To provide a thermal interface 122 formed of a metallic material havingexcellent thermal transfer properties, and yet with minimal voids,thermal interface 122 is injected in a semi-solid or thixotropic state,according to one embodiment.

Thixotropic metal forming processes are also known in the art asrheocasting, semi-solid forging, semi-solid casting, semi-solid forming,slurry-casting, pseudo-plastic casting, thixoforming, thixocasting, orthixomolding. According to this casting method, when certain metalalloys are agitated, they exhibit a significantly low shear strengtheven when they include a relatively high fraction of solid material.Further, as these alloys cool during solidification from a semi-solidstate to a solid state, the resulting solid has a special,non-dendritic, spheroidal microstructure. The non-dendriticmicrostructure of semi-solid metal slurries is described in U.S. Pat.No. 3,902,544.

As used in the metal casting industry, thixoforming provides severalsignificant advantages over ordinary casting methods, including loweroperating temperatures, better laminar cavity fill with less gasentrainment, and less solidification shrinkage. Thixomolding is a knownmethod of casting machine parts using magnesium and zinc alloys,typically utilizing very large and complex casting machinery.

To channel the semi-solid thermally conductive material into the spacebetween die 102 and IHS 120, IHS 120 is specially formed, in oneembodiment, as will be described in greater detail regarding FIGS. 3-5

IC package 100 includes die 102 mounted to lands 106 on the uppersurface of substrate 104 through solder balls or bumps 105. Substrate104 can be a one-layer board or a multi-layer board, and it can includeadditional lands 108 on its opposite side for mating with additionalpackaging structure (not shown). In one embodiment, substrate 104 is anorganic land grid array (OLGA) substrate; however, the embodiments ofthe invention are not limited to use with an OLGA substrate, and anyother type of substrate can be employed. The IC package 100 illustratedin FIG. 2 can form part of electronic assembly 504 shown in FIG. 17 (tobe discussed later). Die 102 can be of any type. In one embodiment, die102 is a processor.

While a BGA arrangement is illustrated in FIG. 2 for coupling die 102 tosubstrate 104, the embodiments of the invention are not limited to usewith a BGA arrangement, and it can be used with any other type ofpackaging technology. Further, the embodiments of the invention are notto be construed as limited to use in C4 packages, and they can be usedwith any other type of IC package where the herein-described features ofthe disclosure provide an advantage.

Die 102 dissipates heat through its upper surface through high capacitythermal interface 122 to combination mold plate and integrated heatspreader (IHS) 120. IHS 120 typically includes a wall or support member110 that extends downward to make physical and thermal contact with theupper surface of substrate 104 through a thermally conductive adhesive(not shown).

To further dissipate heat from IHS 120, a heat sink 114 (optionallyhaving heat fins 116) is often coupled to IHS 120 to dissipate heat intothe ambient environment. Heat sink 114 can be of any suitable shape,material, and size. For increased thermal conductivity between IHS 120and heat sink 114, a thermal interface material 118 can be providedbetween IHS 120 and heat sink 114. In one embodiment, thermal interfacematerial 118 can comprise a thermal gel or grease containing metalparticles.

FIG. 3 illustrates a top view of a combination mold plate and integratedheat spreader (IHS)120, in accordance with one embodiment of theinvention. IHS 120 comprises a relatively thin sheet of thermallyconductive material. In one embodiment, copper or a copper alloy in asquare shape of approximately 37 millimeters (mm) per side and having athickness of approximately 1.5 mm is used. The copper IHS 120 can beplated with a relatively thin layer of nickel. IHS 120 comprises asubstantially planar upper surface. IHS 120 comprises a rectangulardie-mounting or die-fitting area 126 on its lower surface, i.e. thesurface away from the viewer. In one embodiment, die-fitting 126 area isa square of approximately 15 mm per side to accommodate a die ofequivalent dimensions.

IHS 120 further comprises a channel 128 formed across one dimension ofIHS 120 and having a width dimension substantially equal to the widthdimension of the die-fitting area 126. Channel 128 can be formed in IHS120 in any suitable manner. In one embodiment, channel 128 is formed bya metal rolling operation, leaving channel boundaries 124 (see also FIG.5) in the lower surface of IHS 120. Channel 128 could also be formed bycoining, forging, or machining.

Still referring to FIG. 3, IHS 120 further comprises an inlet 132 and anoutlet 134, both of which are apertures in IHS 120. In the embodimentshown, inlet 132 is circular, and outlet 134 is oblong; however, theseshapes are not critical, and any suitable shapes can be used.

IHS 120 further comprises an inlet ramp 133 extending from inlet 132 todie-fitting area 126, and an outlet ramp 135 extending from die-fittingarea 126 to outlet 134. Inlet ramp 133 and outlet ramp 135 are betterseen in FIG. 4, which will now be described.

FIG. 4 illustrates a cross-sectional representation of the combinationmold plate and IHS 120 shown in FIG. 3, taken along dashed line 121 ofFIG. 3. Inlet ramp 133 extends downwardly from inlet 132 to die-fittingarea 126, and outlet ramp 135 extends upwardly from die-fitting area 126to outlet 134. Element 136 is a punched formation formed when inlet 132was partially punched in the IHS 120 plate; similarly, element 138 is apunched formation formed when outlet 134 was partially punched in theIHS 120 plate. Elements 136 and 138 would not be present if inlet 132and outlet 134 were formed via other fabrication processes such asdrilling or molding. Further details concerning the fabrication of IHS120 are provided later regarding FIGS. 8-16.

FIG. 5 illustrates a cross-sectional representation of the combinationmold plate and IHS 120 shown in FIG. 3, taken along dashed line 123 ofFIG. 3. The view in FIG. 5 is looking towards inlet ramp 133, which isdescending from inlet 132 towards the viewer. Also seen in FIG. 5 arethe channel boundaries 124 of channel 128 in the bottom surface of IHS120. The depth of channel 128 can vary, but in general it should be atleast as deep as the desired spacing between the top of the die and thebottom surface of the IHS, e.g. between the top of die 240 and thebottom surface of IHS 230 in FIG. 6, which is discussed immediatelybelow, because the sidewalls of channel 128 serve as mold surfaces toconfine semi-solid metallic material when it is injected into the space236 between the top of die 240 and the bottom surface of IHS 230.

FIG. 6 illustrates a cross-sectional representation of a thermalinterface material (TIM) injection machine 200, in accordance with oneembodiment of the invention, and having a piston 220 in a firstposition.

Injection machine 200 comprises a heated chamber 204 of molten metallicmaterial 206. A feed pipe 208 is coupled to reservoir 202 through acontrol valve 210.

Reservoir 202 has a tubular shape and contains semi-solid metallicmaterial 226. At the lower end of reservoir 202 is an injection nozzle225.

Reservoir 202 also comprises a plunger or piston 220 having a leadingface that conforms to the circular cross-section of reservoir 202 andfurther having an impeller or driver 222 formed of ferromagneticmaterial. In FIG. 6, piston 220 is shown in a raised position, ready tobe impelled downward. An electromagnetic shooting coil 216 surroundsreservoir 202. When shooting coil 216 is actuated, an electromagneticfield is created that quickly impels driver 222 and piston 220 downward.

Reservoir 202 further comprises a suitable agitator to shear and stirthe semi-solid metallic material 226 to the desired thixotropicviscosity. In one embodiment, the agitator comprises one or moreelectromagnetic stirring coils 217 and 218 surrounding reservoir 202. Analternative stirring mechanism could be utilized, such as a screw orauger.

Reservoir 202 also comprises a suitable heating element to maintain thesemi-solid metallic material 226 in a desired semi-solid state. In oneembodiment, heating coils 214, 215, and 219 surround reservoir 202.Heating coils 214, 215, and 219 can be induction heating coils orresistance heating bands.

One of ordinary skill can determine a suitable approximate operatingtemperature range for the semi-solid metallic material 226 by consultinga phase diagram for the particular alloy. In general, one operateswithin a temperature range that provides a relatively greater proportionof solid material than liquid material, and one uses sufficientagitation to prevent the material from solidifying within the reservoir202. In other words, the viscosity is controlled by controlling thetemperature, using heating coils 214, 215, and 219, and by controllingthe agitation, using stirring coils 217 and 218.

Surrounding injection nozzle 225 at the lower end of reservoir 202 is asuitable cooling element. In one embodiment, the cooling elementcomprises one or more water coils 221 into which water can be quicklyintroduced to form a temporary plug 228 of metal within the injectionnozzle 225.

Injection machine 200 further comprises a vacuum chamber 250 having avacuum nozzle 254 and an interior 252 coupled to a vacuum source 256.Vacuum can be provided at vacuum nozzle 254, either constantly or ascontrolled by a suitable actuator valve (not shown). In one embodiment,a vacuum of approximately 15 inches (38.1 centimeters) of mercury isused; however, the amount of vacuum is not critical and can be adjustedto suit specific fabrication requirements.

Injection machine 200 further comprises an IHS retention element 260that is in kept in contact with the upper surface of combination moldplate and IHS 230 through the application of downward force as indicatedby arrow 262.

IHS 230 can be of the same or similar design to IHS 120 shown in FIGS.3-5. Thus IHS 230 has an inlet 232, an outlet 234, an inlet ramp 233,and an outlet ramp 235.

In preparation for a metal injection operation, IHS 230 is positionedadjacent to a die 240, leaving empty space 236 between them. Thispositioning can be done up-line from injection machine 200. A temporaryjig (not shown) can be used, if necessary, to maintain die 240 theproper distance from IHS 230; alternatively, a suitable standoff couldbe fabricated from IHS 230 itself. The assembly is then moved toinjection machine 200, where the IHS retention element 260 is lowered tohold down IHS 230.

IHS 230 and/or injection nozzle 225 and vacuum nozzle 254 are thensubsequently moved relative to each other, so that injection nozzle 225is adjacent to inlet 232, and vacuum nozzle 254 is adjacent to outlet234. Which elements are moved with respect to each other is notessential, and in various embodiments, these elements can be movedrelative to each other in any suitable manner. The injection ofsemi-solid metallic material into space 236 will now be described withreference to FIG. 7.

FIG. 7 illustrates a cross-sectional representation of a TIM injectionmachine 200, in accordance with one embodiment of the invention, andhaving a piston 220 in a second position.

To inject semi-solid metallic material into space 236 between IHS 230and die 240, the following sequence of events occurs, not necessarily inthe order given. Vacuum is turned on (in an embodiment wherein vacuum isturned on and off, as opposed to being constantly on) at vacuum nozzle254 to lower the air pressure in the space 236 between die 240 and IHS230. Stirring of semi-solid metallic material 226 (refer back to FIG. 6)within reservoir 202 is stopped.

Still referring to FIG. 7, cold water circulating in water coil 221 isstopped, and heating coils 219 near injection nozzle 225 are turned on,thus melting the temporary plug 228 (refer back to FIG. 6) residing inthe opening of injection nozzle 225. In other embodiments, temporaryplug 228 could be melted either by stopping the circulation of coldwater in water coil 221 or by heating coils 219, but not necessarilyboth, depending upon the thermal characteristics of the injection nozzle225 and the semi-solid metallic material within reservoir 202.

Still referring to FIG. 7, control valve 210 is closed, and shootingcoil 216 is actuated, quickly forcing driver 222 of piston 220 downwardthrough reservoir 202. This squirts semi-solid metallic material 227through injection nozzle 225 into inlet 232 and into the space 236between die 240 and IHS 230. The semi-solid metallic material ischanneled and confined on the bottom by inlet ramp 233, the uppersurface of die 240, and by outlet ramp 235. The semi-solid metallicmaterial is confined on the top by combination mold plate and IHS 230,which is held down by IHS retention element 260.

The semi-solid metallic material quickly fills the space 236, aided byvacuum applied by vacuum source 256 through vacuum nozzle 254 adjacentto and in contact with outlet 234. In some embodiments, the vacuum caneliminate or reduce the need for fluxes, due to the superior wetting andflow characteristics provided by the vacuum.

The injected semi-solid metallic material cools quickly. In oneembodiment, cooling can be hastened by cooling the IHS retention element260. After cooling, the injected semi-solid metallic material has becomea solidified thixotropic material.

The term “solidified thixotropic material”, as used herein, means asolidified material that was in thixotropic state just prior tosolidification and that exhibits a non-dendritic structure.

To complete the fill cycle, vacuum can be turned off to vacuum nozzle254 (in an embodiment in which vacuum is controlled, as opposed to beingon constantly), and water can be introduced to form another temporaryplug 228 (refer to FIG. 6) of metal within the injection nozzle 225.Still referring to FIG. 7, injection nozzle 225 and vacuum nozzle 254are withdrawn from IHS 230. IHS retention element 260 is withdrawn fromthe upper surface of IHS 230. The IC package assemblies in thefabrication line are then incremented by moving the current IC packageassembly out and moving a new IC package assembly into the injectionmachine 200.

After injection, piston 220 is withdrawn upwards by reversing theshooting coil 216. After piston 220 passes pipe 208, control valve 210is quickly reopened, and additional molten metallic material 206 issupplied into reservoir 202 from heated chamber 204. The cycle thenstarts over as shown in FIG. 6.

FIG. 8 illustrates a top view of a metal sheet having a central troughor channel 304, representing a stage in the fabrication of a combinationIHS and mold plate 300, in accordance with one embodiment of theinvention. In one embodiment, the metal sheet comprises copper or acopper alloy, and the metal sheet is approximately 1.5 mm in thicknessand approximately 37 millimeters (mm) per side. However, the thicknessand size are not at all critical, and many other dimensions could beused, depending upon the desired IC package geometry.

Channel 304 can be formed in any suitable manner. In one embodiment,channel 304 is formed by a metal rolling operation, leaving channelboundaries 302 and 303 in the surface of the plate that will become IHS300. Channel 304 could also be formed in any other suitable manner, e.g.by coining, forging, or machining. As viewed in FIG. 8, channel 304 islower than the region situated above channel boundary 302 or the regionsituated below channel boundary 303. The opposite side of the plate canbe substantially planar.

FIG. 9 illustrates a cross-sectional representation of a fabricatingmachine 310 having metal punches 312 and 314 in a first positionrelative to the partially fabricated IHS 300 shown in FIG. 8, inaccordance with one embodiment of the invention.

The channeled metal sheet shown in FIG. 8 is inverted and placed ontothe base 311 of fabricating machine 310. Base 311 has a cut-out section316 for receiving partially fabricated IHS 300, including a raisedportion (not seen) for supporting channel 304 (refer back to FIG. 8).Still referring to FIG. 9, base 311 can comprise a resilient material toabsorb the force of punching forces applied to punches 312 and 314 inthe direction of arrows 317 and 318, respectively; alternatively, base311 can comprise cut-out sections (not shown) of the proper shape anddepth to receive the partially punched segments 320 and 322 (refer toFIG. 10) when punches 312 and 314 are driven down. Punches 312 and 314are contained within punch sleeves 313 and 315, respectively.

FIG. 10 illustrates a cross-sectional representation of a fabricatingmachine 310 having metal punches 312 and 314 in a second positionrelative to partially fabricated IHS 300, in accordance with oneembodiment of the invention. Punching forces in the direction indicatedby arrows 317 and 318 are actuated to drive punches 312 and 314,respectively, into partially fabricated IHS 300. As a result, segments320 and 322 are partially driven through by punches 312 and 314,respectively.

FIG. 11 illustrates a cross-sectional representation of a partiallyfabricated IHS 300, representing an intermediate stage in thefabrication of a combination mold plate and IHS 300, in accordance withone embodiment of the invention. As seen in FIG. 11, partiallyfabricated IHS 300 now comprises partial holes 332 and 334 in what isnow the upper surface of partially fabricated IHS 300. Partial holes 332and 334 are better viewed in FIG. 12, which will now be described.

FIG. 12 illustrates a top view of the partially fabricated IHS 300 shownin FIG. 11. Partial hole 332 is round, while partial hole 334 is oblong.The round partial hole 332 should be properly sized to fit the injectionnozzle (225, FIG. 6) of the injection machine. The oblong partial holeshould be properly sized to fit the vacuum nozzle (254, FIG. 6)according to the amount of vacuum required to rid the semi-solidmetallic material of entrapped air. Partial holes 332 and 334 are in thesurface of partially fabricated IHS 300 towards the viewer. The surfaceaway from the viewer comprises channel 304, which has channel boundaries302 and 303.

Although in this fabrication sequence, the channel 304 is described asbeing formed prior to punching partial holes 332 and 334, in anotherembodiment, the channel could be formed concurrently with or followingthe formation of partial holes 332 and 334.

FIG. 13 illustrates a cross-sectional representation of a skiving tool344 of a skiving machine 340 being employed on the partially fabricatedIHS 300 shown in FIG. 12, in accordance with one embodiment of theinvention. Skiving machine 340 comprises a base 341 having raised mounts342 and 343. From the orientation shown in FIG. 11, partially fabricatedIHS 300 is inverted and positioned on the base 341 so that raised mounts342 and 343 fit into partial holes 332 and 334, respectively.

Skiving tool 344 is driven in the direction indicated by arrow 345, andit peels up inlet ramp 351 from the upper surface of partiallyfabricated IHS 300. Skiving tool 344 cuts through partial hole 332, sothat a complete hole is now formed, as viewed from the underside ofpartially fabricated IHS 300.

In a similar operation, skiving tool 344 is rotated 180 degrees andmoved in a direction opposite to that indicated by arrow 345 to peel upthe outlet ramp 353 (refer to FIG. 14). Alternatively, the jig andpartially fabricated IHS 300 could be rotated 180 degrees for thisoperation. Which element is moved with respect to another is notessential, and in various embodiments, these elements can be movedrelative to each other in any suitable manner.

FIG. 14 illustrates a cross-sectional representation of an intermediatestage in the fabrication of a combination mold plate and IHS 300, inaccordance with one embodiment of the invention. In FIG. 14, both sidesof partially fabricated IHS 300 have undergone a skiving operation.Inlet ramp 351, including inlet ramp tip 352, are shown on the left-handside of partially fabricated IHS 300, and outlet ramp 353, includingoutlet ramp tip 354, are shown on the right-hand side of partiallyfabricated IHS 300. Also seen in FIG. 14 is a depression 355corresponding to the inlet ramp 351 lifted by the skiving blade. Theentry point 356 made by the skiving blade, at the inlet ramp tip 352, isalso shown. Similarly, a depression 357 and entry point 358 are shownfor outlet ramp 353 and outlet ramp tip 354, respectively.

FIG. 15 illustrates a top view of the partially fabricated IHS 300 shownin FIG. 14. In FIG. 15 are seen the partially completed inlet ramp 351and partially completed outlet ramp 353 extending outwardly towards theviewer.

FIG. 16 illustrates a cross-sectional representation of a fabricatingmachine 400 employing a stamping tool 401 on the partially fabricatedIHS 300 shown in FIG. 14, in accordance with one embodiment of theinvention. Fabricating machine 400 comprises a base 410 having raisedmounts 411 and 412 that fit into holes 332 and 334, respectively, ofpartially fabricated IHS 300.

Stamping tool 401 comprises an embossed surface 402. A forming plate orspacing shoe 413 is placed under partially formed inlet ramp 351.Stamping tool 401 is then forced downward in the direction indicated byarrow 403. As a result, inlet ramp 351 is completely formed in thesubstantially planar shape indicated by inlet ramp 133 of IHS 120 (referto FIG. 4).

Still referring to FIG. 16, in similar fashion, a forming plate orspacing shoe 414 is placed under partially formed outlet ramp 353, andan appropriately embossed stamping tool (not shown) is used to finishshaping outlet ramp 353 in the substantially planar shape indicated byoutlet ramp 135 of IHS 120 (refer to FIG. 4).

FIG. 17 is a block diagram of an electronic system 500 incorporating atleast one electronic assembly 504 with a high capacity thermal interfacein accordance with one embodiment of the invention. Electronic system500 is merely one example of an electronic system in which an embodimentof the invention can be used. In this example, electronic system 500comprises a data processing system that includes a system bus 502 tocouple the various components of the system. System bus 502 providescommunications links among the various components of the electronicsystem 500 and can be implemented as a single bus, as a combination ofbusses, or in any other suitable manner.

Electronic assembly 504 is coupled to system bus 502. Electronicassembly 504 can include any circuit or combination of circuits. In oneembodiment, electronic assembly 504 includes a processor 506 which canbe of any type. As used herein, “processor” means any type ofcomputational circuit, such as but not limited to a microprocessor, amicrocontroller, a complex instruction set computing (CISC)microprocessor, a reduced instruction set computing (RISC)microprocessor, a very long instruction word (VLIW) microprocessor, agraphics processor, a digital signal processor (DSP), or any other typeof processor or processing circuit.

Other types of circuits that can be included in electronic assembly 504are a custom circuit, an application-specific integrated circuit (ASIC),or the like, such as, for example, one or more circuits (such as acommunications circuit 507) for use in wireless devices like cellulartelephones, pagers, portable computers, two-way radios, and similarelectronic systems. Electronic assembly 504 can perform any other typeof function. Electronic assembly 504 can comprise a single IC ormultiple ICs.

Electronic system 500 can also include an external memory 510, which inturn can include one or more memory elements suitable to the particularapplication, such as a main memory 512 in the form of random accessmemory (RAM), one or more hard drives 514, and/or one or more drivesthat handle removable media 516 such as floppy diskettes, compact disks(CDs), digital video disk (DVD), and the like.

Electronic system 500 can also include a display device 508, one or morespeakers 509, and a keyboard and/or controller 520, which can include amouse, trackball, game controller, voice-recognition device, or anyother device that permits a system user to input information into andreceive information from the electronic system 500.

FIG. 18 is a flow diagram of a method of forming thermally conductivematerial between an IC and a plate, in accordance with one embodiment ofthe invention. The plate can be a combination mold plate and IHS, suchas IHS 120 shown in FIGS. 3-5. The method starts at 600.

In 602, a thermally conductive material is agitated within an injectionmachine. The thermally conductive material can be a liquid metallicmaterial or a semi-solid metallic material. The thermally conductivematerial can comprise an alloy from the group consisting essentially oftin, lead, silver, gold, nickel, copper, antimony, zinc, indium,bismuth, and gallium. In one embodiment, an alloy of approximately 63%tin and 37% lead is used. The thermally conductive material can alsocomprise a pure metal from the group consisting essentially of tin,lead, silver, gold, nickel, copper, antimony, zinc, indium, bismuth, andgallium, in which case the melting point can be expected to be higherthan that of an alloy.

In 604, a die is positioned adjacent to a plate.

In 606, the thermally conductive material is flowed between the die andthe plate.

In 608, vacuum is concurrently applied to the thermally conductivematerial to assist in flowing it between the die and the plate. Inanother embodiment, vacuum is applied before or after the thermallyconductive material is flowed between the die and the plate. In yetanother embodiment, vacuum is not used. The method ends at 610.

FIGS. 19A and 19B together illustrate a flow diagram of a method ofoperating a machine to form thermally conductive material between an ICand a mold plate, in accordance with one embodiment of the invention.The mold plate can be a combination mold plate and IHS, such as IHS 120shown in FIGS. 3-5. The method starts at 700.

In 702, a mold plate is positioned adjacent to a die. The mold platecomprises an inlet and an outlet. The mold plate and die are adjacent toan injection machine. The injection machine comprises a reservoir ofsemi-solid metallic material, an injection nozzle, a suction or vacuumnozzle, and a heating element. The injection machine farther comprises apressure source. In one embodiment, the pressure source comprises ashooting coil surrounding the reservoir. The injection machine alsocomprises a vacuum source to couple to the vacuum nozzle. In addition,the injection machine comprises an agitator to stir the semi-solidmetallic material. In one embodiment, the agitator comprises at leastone stirring coil surrounding the reservoir.

In 704, the semi-solid metallic material is stirred using the agitator.

In 706, the injection nozzle is moved adjacent to the inlet.

In 708, the vacuum nozzle is moved adjacent to the outlet.

In 710, the heating element is turned on.

In 712, the vacuum nozzle is coupled to the vacuum source.

In 714, semi-solid metallic material is flowed through the injectionnozzle and inlet to substantially occupy a space between the mold plateand the die. In one embodiment, this is carried out by activating ashooting coil to cause a piston to force the semi-solid metallicmaterial through the injection nozzle. The method ends at 716.

The operations described above with respect to the methods illustratedin FIGS. 18, 19A, and 19B can be performed in a different order fromthose described herein. Further, some operations can be eliminated orcombined with other operations. In addition, some operations may overlapwith other operations.

FIGS. 1-16 are merely representational and are not drawn to scale.Certain proportions thereof may be exaggerated, while others may beminimized. FIGS. 2-19B are intended to illustrate variousimplementations of the invention that can be understood andappropriately carried out by those of ordinary skill in the art.

The above-described composition, geometry, dimensions, elements, andorder of operations are merely exemplary of the embodiments illustrated,and they are not meant to be limiting. They can all be varied by one ofordinary skill in the art to optimize the thermal performance of thepackage, as well as the fabrication of the package.

For example, in place of a combination mold plate and IHS formed ofcopper, an IHS formed of diamond could be substituted. In suchembodiment, an inlet and outlet would not necessarily be made in theIHS, and the semi-solid metallic material could be injected into oneside of the cavity between the die and the IHS. Suitable restraintsand/or molds could be employed to confine the semi-solid metallicmaterial within the cavity between the upper surface of the die and thelower surface of the diamond IHS. Further, such restraints and/or moldscould be used with an IHS formed of another type of material, such ascopper or a copper alloy, in which case the IHS would not require aninlet, an outlet, an inlet ramp, or an outlet ramp.

In other embodiments, the combination mold plate and IHS can compriseother materials with thermal qualities that are only slightly inferiorto diamond, such as a diamond composite, or graphite. A suitable diamondcomposite can comprise a mixture of diamond particles and particles ofanother substance, such as aluminum or copper.

An IHS fabricated of diamond, diamond composite, or graphite could havea suitable plating of metal, such as titanium, chromium, tungsten, ormolybdenum, to enhance adhesion.

In addition, although a semi-solid metallic material has been described,a totally liquid metallic material could also be used in otherembodiments.

Although a coil-operated piston arrangement has been disclosed as apressure source in injection machine 200 (FIGS. 6 and 7), other suitablepressure sources could be substituted, such as a hydraulic or pneumaticpressure source, a cam or lever, or the like.

Further, the arrangement of stirring coils and shooting coils can bevaried. For example, multi-function coils could be provided that performboth stirring and shooting. In another embodiment, one set of stirringcoils could rotate the semi-solid metallic material in one direction,and another set of stirring coils could rotate it in the oppositedirection. More or fewer stirring and/or shooting coils could beprovided than are illustrated.

A rotating piston or a rotating internal rod could be used to stir thesemi-solid metallic material.

The injection nozzle and vacuum nozzle could be coated with ceramic orother suitable material to reduce metal wetting and wear.

The embodiments of the invention provide for an electronic assembly andmethods of manufacture thereof that minimize thermal dissipationproblems associated with high power delivery. An electronic systemand/or data processing system that incorporates one or more electronicassemblies that utilize the features of the present disclosure canhandle the relatively high power densities associated with highperformance integrated circuits, and such systems are therefore morecommercially attractive.

By substantially increasing the thermal dissipation from highperformance electronic assemblies, such electronic equipment can beoperated at increased clock frequencies. Alternatively, such equipmentcan be operated at reduced clock frequencies but with lower operatingtemperatures for increased reliability.

As shown herein, the invention can be implemented in a number ofdifferent embodiments, including a combination mold plate and IHS, anelectronic assembly, an electronic system in the form of a dataprocessing system, a metallic material injection machine, and variousmethods of fabricating the combination mold plate and IHS, fabricatingthe electronic assembly, and operating the injection machine. Otherembodiments will be readily apparent to those of ordinary skill in theart. The elements, materials, geometries, dimensions, and sequence ofoperations can all be varied to suit particular packaging requirements.

While certain operations have been described herein relative to “upper”and “lower” surfaces, “left” and “right”, and “front” and “back”, itwill be understood that these descriptors are relative, and that theywould be reversed if the IC package were inverted or rotated ormirrored. Therefore, these terms are not intended to be limiting.

It is emphasized that the Abstract is provided to comply with 37 C.F.R.§1.72(b) requiring an Abstract that will allow the reader to quicklyascertain the nature and gist of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims.

In the foregoing Detailed Description, various features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments of the inventionrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed embodiment. Thus the followingclaims are hereby incorporated into the Detailed Description ofEmbodiments of the Embodiments, with each claim standing on its own as aseparate preferred embodiment.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. This application isintended to cover any adaptations or variations of embodiments of theinvention. Therefore, it is manifestly intended that the inventionembodiments be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. An integrated circuit (IC) package comprising: adie having a front surface comprising a plurality of terminals, and thedie further having a back surface; a plate positioned over the backsurface of the die; and a thermally conductive element coupled betweenthe die and the plate, the thermally conductive element comprising asolidified thixotropic metal alloy material.
 2. The IC package recitedin claim 1 wherein the material comprises an alloy from the groupconsisting essentially of tin, lead, silver, gold, nickel, copper,antimony, zinc, indium, bismuth, and gallium.
 3. The IC package recitedin claim 1 wherein the material comprises an alloy of approximately 63%tin and 37% lead.
 4. The IC package recited in claim 1 wherein the platecomprises an inlet and an outlet.
 5. The IC package recited in claim 4wherein the plate comprises an inlet ramp and an outlet ramp.
 6. The ICpackage recited in claim 5 wherein the inlet ramp extends from the inletto the die, and wherein the outlet ramp extends from the die to theoutlet.
 7. The IC package recited in claim 1 and further comprising: asubstrate; and a wall coupled to the plate and comprising a surfacecoupled to the substrate.
 8. The IC package recited in claim 7 whereinthe substrate is an organic substrate and wherein the die is positionedon the substrate through a land grid array.
 9. The IC package recited inclaim 1 and further comprising: a heat sink coupled to the plate. 10.The IC package recited in claim 9 and further comprising: a thermalinterface material between the plate and the heat sink.
 11. The ICpackage recited in claim 1 wherein the plate comprises one of copper ora copper alloy.
 12. The IC package recited in claim 1 wherein the platecomprises diamond.
 13. The IC package recited in claim 1 wherein theplate comprises a channel having a dimension substantially equal to adimension of the die.
 14. An integrated circuit (IC) package comprising:a die having a front surface comprising a plurality of terminals, andthe die further having a back surface; a plate adjacent to the backsurface of the die; and a solidified thixotropic metal alloy materialbetween the die and the plate.
 15. The IC package recited in claim 14wherein the material comprises an alloy from the group consistingessentially of tin, lead, silver, gold, nickel, copper, antimony, zinc,indium, bismuth, and gallium.
 16. The IC package recited in claim 14wherein the plate comprises an inlet, an outlet, an inlet ramp, and anoutlet ramp, and wherein the inlet ramp extends from the inlet to thedie, and wherein the outlet ramp extends from the die to the outlet. 17.The IC package recited in claim 14 and further comprising: a substrate;and a wall coupled to the plate and comprising a surface contacting thesubstrate.
 18. The IC package recited in claim 17 wherein the substrateis an organic substrate and wherein the die is positioned on thesubstrate through a land grid array.
 19. The IC package recited in claim14 and further comprising a heat sink coupled to the plate through athermal interface material.
 20. The IC package recited in claim 14wherein the plate comprises one of copper, a copper alloy, and diamond.21. The IC package recited in claim 14 wherein the plate comprises achannel having a dimension substantially equal to a dimension of thedie.
 22. An integrated circuit (IC) package comprising: a die; a plateadjacent to the die and including a substantially planar upper surface alower surface comprising a die-fitting area having equivalent dimensionsto those of the die, and having a pair of boundaries in physical contactwith the die; an inlet in the upper surface; an outlet in the uppersurface; an inlet ramp extending downwardly from the inlet to thedie-fitting area and in physical contact with both the inlet and thedie-fitting area; and an outlet ramp extending upwardly from thedie-fitting area to the outlet and in physical contact with both thedie-fitting area and the outlet; and a solidified material between thedie and the plate formed by flowing a thermally conductive materialbetween the die and the plate.
 23. The IC package recited in claim 22,wherein the plate further comprises a channel having a dimensionsubstantially equal to a dimension of the die-fitting area.
 24. The ICpackage recited in claim 22, wherein the plate is formed of materialcomprising one of copper, a copper alloy, and diamond.
 25. The ICpackage recited in claim 22, wherein the die comprises a processor. 26.A package comprising: a die having a front surface comprising aplurality of terminals, and the die further having a back surface; aplate adjacent to the back surface of the die; and a solidifiedthixotropic metal alloy material between the die and the plate formed byflowing a thermally conductive semi-solid metal alloy material betweenthe die and the plate.
 27. The package recited in claim 26, wherein theplate comprises: a substantially planar upper surface a lower surfacecomprising a die-fitting area; an inlet in the upper surface; an outletin the upper surface; an inlet ramp extending from the inlet to thedie-fitting area; and an outlet ramp extending from the die-fitting areato the outlet.
 28. The package recited in claim 26, wherein the materialcomprises an alloy selected from the group consisting essentially oftin, lead, silver, gold, nickel, copper, antimony, zinc, indium,bismuth, and gallium.
 29. The package recited in claim 28, wherein thematerial comprises an alloy of approximately 63% tin and 37% lead.